It's getting hard to keep a place on the list of the world's fastest supercomputers.

The Top500 ranking of supercomputers, released twice a year by researchers at the universities of Tennessee and of Mannheim, Germany, experienced heavy turnover, with faster new arrivals bumping 220 lesser systems off the list. The minimum performance necessary to keep a place on the list increased 42 percent from November 2001--the biggest jump in three years.

The arrival of NEC's top-ranked Earth Simulator in Japan has reworked the top of the list, but there's also plenty of action lower down in the rankings, where systems are affordable enough to be bought by multinational corporations, not just lavishly funded government research programs into nuclear weapons or weather.

These less exotic supercomputers are used by telecommunications, financial services and automotive companies. Here, Hewlett-Packard's Superdome machine is common, while IBM's newer p690 "Regatta" model is beginning to make its presence felt.

Superdomes take up all but two spots between Nos. 279 and 353. These are 128- to 96-processor systems purchased by BMW, Cisco Systems, France Telecom, Verizon Communications, Vodafone Group, Brasil Telecom, Bell Canada, Starbucks, General Electric, Sprint PCS and others. For IBM, newer p690 systems using Big Blue's Power4 processor are beginning to encroach on the numerous earlier Power3-based servers.

The Top500 list is based on a performance yardstick called Linpack, a calculation that represents only some aspects of supercomputer capability. In an effort to create a better benchmark, though, market research firm IDC, along with the Top500 organizers and supercomputer sellers, has created a different list intended to be a more accurate reflection of real-world performance.

The IDC "Balanced Rating" measures parameters such as how fast data can be transferred from one part of the system to another. The Linpack measurement, by comparison, is more a reflection of processor speed and count, which isn't always a reflection of how well a computer can simulate, say, all the physics of a car crash. A side-by-side comparison of the two lists' rankings is difficult because IDC groups its rankings into four categories based on price criteria, a factor the Top500 list doesn't include.

Through its $19 billion merger with Compaq Computer, HP now gets credit for some high-ranking systems and has the most on the overall Linpack-based list: 168 machines. IBM, close behind with 164 systems, boasts the largest fraction of the total computing power represented by the entire 500 list: 33.3 percent to HP's 22.2 percent and NEC's 19 percent.

IBM hopes to gain in the supercomputer market, however, and announced two major new customers Thursday. The U.S. Defense Department's Naval Oceanographic Office has purchased a system called Blue Ocean that will link 1,184 processors in 37 p690 servers. The High-Performance Computing Center for North Germany, meanwhile, will buy a p690-based that will be about two-thirds that powerful.

Both these systems would rank in the top four of the current list, as would a National Weather Service system now being installed.

Big Blue is aggressively funding two major types of supercomputer research: first, its expensive Unix servers linked together with a high-speed "SP" switch, and second, larger numbers of less expensive computers using Intel processors and the Linux operating system.

IBM dominates when it comes to systems--called "Beowulf" supercomputers--based on this latter approach. A total of 49 of the Top500 systems are such clusters, with 31 of them built by IBM. But the top-performing Beowulf cluster, a 512-processor machine at the University of Heidelberg in Germany, was built by Megware and uses Advanced Micro Devices processors. It ranks No. 35 on the list.

Beowulf clusters have also given Dell Computer a place on the list. A system with 256 Intel Xeon processors at Sandia National Laboratories, the lab affiliated with the U.S. Department of Energy's National Nuclear Security Administration, ranks at 79. Dell, not known for its engineering prowess, also has two lesser systems on the list.

At the top end of the spectrum, the energy department's nuclear weapons simulation program has underwritten many systems. The program, formerly called the Accelerated Strategic Computing Initiative but now called the Advanced Simulation and Computing (ASC) program, was launched to let computers take on the challenge of testing nuclear weapons without actually exploding them.

The ASC program has funded the systems at Nos. 2, 6, 7, 9, 11, and 15. In addition, the French nuclear weapons program funded the No. 4 machine, and the United Kingdom's nuke program placed its machine at No. 11.

The number of computers that can perform more than 1 trillion calculations per second has risen from 17 to 23.

At the top of the heap, though, is NEC's Earth Simulator, which models climate change, plate tectonics and other phenomena. Occupying roughly four tennis courts' worth of space, the system churns out 35.9 trillion calculations per second, making its performance larger than that of the next 12 systems combined. The Earth Simulator also surpasses the output of the entire 500-computer list from November 1998, the organization said.